1. Field of the Invention
The present invention relates to a light-emitting device, and more particularly to a light-emitting device with a color-filter-on-array structure.
2. Description of the Related Art
With recent interests and development, organic light-emitting diode (OLED) devices have become a potential candidate to replace Liquid Crystal Displays (LCDs) for next-generation display. With their active light-emitting characteristics, OLED devices, unlike LCDs, do not require a backlight module to provide a light source, benefiting their weight reduction. In addition, OLED devices provide high resolution and quick response, and a wider viewing angle (to 160°) than LCDs.
OLED devices utilize an organic light-emitting diode to provide the light source. The organic light-emitting diode uses an organic layer as an active layer, sandwiched between an anode and cathode electrodes to form a stacked layer. At least one of the electrodes is transparent to allow light transmission.
FIG. 1 is a cross-section view of a conventional OLED device. The OLED device 1 includes a substrate 2, monochromatic light-emitting diodes 3, and thin film transistors 20. Monochromatic light emitted from a active layer 30 of the light-emitting diodes 3 converts to red, green or blue light respectively after passing through a red 81, green 82, or blue 83 color-filtering unit. The substrate 2 is a transparent substrate of, for example, glass or polymer. As a polymeric substrate, the substrate 200 can be made of polyethyleneterephthalates, polyesters, polycarbonates, polyacrylates or polystyrenes. Furthermore, the color-filtering unit is formed by, for example, pigment dispersion, dyeing, electrodeposition, or printing
In FIG. 1, an indium-tin-oxide (ITO) layer is formed over the substrate 2 to serve as a transparent anode 31, with a counter cathode electrode 32 of a low-work-function metal or alloy, such as Ca, Al, MgAg or AlLi.
In the conventional OLED device, the color-filtering units 81, 82 and 83 generally have severe surface roughness Ra around 20 nm. If the transparent anode electrode 31 is directly formed on the color-filtering units 81, 82 and 83, the surface roughness of the transparent anode electrode 31 is definitely affected, thereby resulting in a surface roughness also around 20 nm. In addition to failure to fulfill the requirements of an OLED device (preferred surface roughness of the electrode less than 10 nm), short circuit and current-leakage may also be caused, deteriorating performance.
To avoid the above shortcomings, a additional planarization layer 5 must be placed between the transparent electrode 31 and the color-filtering units 81, 82 and 83, to avoid the inherent surface roughness of color-filtering units 81, 82 and 83 affecting subsequent electrode formation. However, the process complexity is increased, resulting in high manufacturing costs and time-consuming.
Therefore, it is necessary to develop a simple and efficient manufacturing method for an OLED with a color-filter-on-array structure to obtain OLEDs having smoother transparent electrode surfaces.